Macromolecules 1983, 16, 452-456
452
combinations of incident and scattered polarizations with those predicted by group theoretical analysis of an isolated in either a 3/2-he1ical Or P1anar-zigze conformation* Observation of the Raman-active LAM and the correlation of its position with the corresponding stem length in lamellar crystals provide further evidence of a transplanar structure. Combined infrared and Raman measurements in the CH stretching region indicate, based on local symmetry arguments, that the CC bond joining the two CH2groups must be trans* this a necessary but not sufficient condition for planarity, when taken collectively with the additional results already described, it strongly supports the existence of a planar structure for the E-TFE copolymer in the solid state, as has been predicted by Farmer and Lando.14
Acknowledgment. We thank E. s. Clark (University of Tennessee) and T. Russell (IBM) for obtaining the wfis and SAXS photographs of the E-TFE copolymer filament. Registry No. E-TFE, 25038-71-5.
References and Notes (1) Carter, V. B. J. Mol. Spectrosc. 1970, 34, 356. (2) Bailey, R. T.; Hyde, A. J.; Kim, J. J. Spectrochim. Acta, Part A 1974,30A, 91. (3) Boerio, F. J.; Bailey, R. A. J . Polym. Sci., Polym. Lett. Ed. 1974, 12, 433. (4) Bailey, R. T.; Hyde, A. J.; Kim, J. J.; McLeish, J. Spectrochim. Acta, Part A 1977, 33A, 1053. (5) Rabolt, J. F.; Fanconi, B. Macromolecules 1978, 11, 740. (6) Satija, S.; Wang, C. H. J . Chem. Phys. 1978, 69, 2739. (7) Abenoza, M.; Armengaud, A. Polymer 1981,22, 1341. (8) Modena, M.; Garbuglio, C.; Ragazzini, M. J. Polym. Sci., Polym. Lett. Ed. 1972, 10, 153.
(9) Pireaux, J. J.; Riga, J.; Caudano, R.; Verbist, J.; Gobillon, Y.; Delhalle, J.; Delhalle, S.; Andre, J. M. J. Polym. Sci., Part A-I 1979, 17, 1175. (10) English, A. D.;Garza, 0. T. Macromolecules 1979, 12, 351. (11) Clark, D. T.; Feast, W. J.; Ritchie, I.; Musgrave, W. K. R.; Modena, M.; Ragazzini, M. J. Polym. Sci., Part A-1 1974,12, 1049. (12) Garbuglio, C.; Modena, M.; Valera, M.; Ragazzini, M. EUF. Polym. J. 1974, 10, 91. (13) Wilson, F. C.; Starkweather, H. W., Jr. J . Polym. Sci., Part A-2 1973, 11, 919. (14) Farmer, B. L.; Lando, J. B. J. Macromol. Sci., Phys. 1975, B I I , 89 (15) D&lin, G. E.; Davis, J , L.; Chase, L.;Geschwind, S. Appl. Phys. Lett. 1971, 19, 138. (16) Snyder, R. G.; Scherer, J. R. J . Polym. Sci., Part A-2 1980,18, 421. (17) Billmeyer, F. W., Jr. In “Textbook of Polymer Science”;Wiley: New York, 1971. (18) Kobayashi, M.; Tashiro, K.; Tadokoro, H. Macromolecules 1975, 8, 158. (19) Alexander, L. E. In “X-Ray Diffraction Methods in Polymer Science”; Wiley-Interscience: New York, 1969. (20) Damen, T. c.;Port9 s. p. s.;Tell, B. PhYS. Rev. 1966, 142, 570. (21) Snyder, R. G. J . Mol. Spectrosc. 1971, 37, 353. (22) Schlotter, N. E.; Rabolt, J. F., to be published. (23) Hsu, S. L.; Sibilia, J. P.; Obrien, K. P.; Snyder, R. G. Macromolecules 1978, 11, 990. (24) Hendra, P. J.; Jobic, H. P.; Marsden, E. P.; Bloor, D. Spectrochim. Acta, Part A 1977,33A, 445. (25) Campos-Vallette, M.; Rey-Lafon, M. J . Chem. Phys., in press. (26) Strobl, G. R.; Hagedorn, W. J . Polym. Sci., Part A-2 1978, 16, 1181.
(27) Fanconi, B.; Crissman, J. J. Polym. Sci., Polym. Lett. Ed. 1975, 13, 421. (28) Shimanouchi, T.; Tasumi, M. Indian J . Pure Appl. Phys. 1971, 9, 958. (29) Reneker, D. H.; Fanconi, B. J . Appl. Phys. 1975, 48, 4144. (30) Schaufele, R. F.; Shimanouchi, T. J . Chem. Phys. 1967, 47, 3605. (31) Rabolt, J. F.; Fanconi, B. Polymer 1977, 18, 1258.
Effect of Polymer Chain Tacticity on the Fluorescence of Molecular Rotors Rafik 0. Loutfy* Xerox Research Centre of Canada, 2480 Dunwin Drive, Mississauga, Ontario L5L lJ9,Canada
David M. Teegarden’ Webster Research Center, Xerox Corporation, Webster, New York 14580. Received January 14, 1982
ABSTRACT: The fluorescence properties of julolidinemalononitrile (l),a molecular rotor probe, have been studied in a series of stereoregular poly(methy1 methacrylate) films. The quantum yield of fluorescence of 1 was found t o be dependent on the tacticity of the polymer. The relatively high fluorescence yield of 1 in isotactic PMMA indicated that the flexibility of isotactic chains is lower than that of syndiotactic or atactic PMMA. The temperature-dependent fluorescence results are consistent with a helical conformation for isotactic PMMA.
In recent years methods have become known for the preparation of high molecular weight stereoregular isotactic and syndiotactic poly(methy1 methacrylate) ,l (i- and sPMMA) (see Figure 1). These species exhibit vastly different properties from the so-called atactic (a-PMMA) or random polymers. Both the isotactic and syndiotactic Present address: Department of Chemistry, St. John Fisher College, Rochester, NY 14618. 0024-9297/83/2216-0452$01.50/0
PMMA polymers have been characterized through differences in X-ray diffraction patterns,2 infrared ~ p e c t r a , ~ laser Raman ~ p e c t r afar-ultraviolet ,~ spectra,” densities? glass transition temperature,6 dielectric loss curve^,^ and mechanical and viscoelastic properties.8 Information on the steric arrangements of functional groups is best provided by high-resolution NMR technique^.^ Although certain of these measurements have given direct information on the tacticity of these polymers, the 0 1983 American Chemical Society
Macromolecules, Vol. 16, No. 3, 1983
ISOTACTlC
order of 10'l sal. T h e extremely fast deactivation r a t e of t h e singlet s t a t e of these materials was attributed t o torsional relaxation, W e have shown that environmental factors restricting t h e internal molecular rotation of these dyes lead to a decrease in I t , a n d consequently an increase in fluorescence yield. These dyes are, therefore, excellent microscopic probes for measuring t h e torsional rigidity of t h e surrounding polymer media, a n d their fluorescence yield is very sensitive t o dynamic structural changes occurring over wide temperature range. H e r e t h e results of a n investigation concerning t h e emission properties of julolidinemalononitrile (1) in solid
p
043
SYNDIOTACTIC
Effect of Polymer Chain Tacticity on Fluorescence 453
\
n
H
1 films of stereoregular poly(methy1 methacrylate) are reported. T h e q u a n t u m yield of fluorescence of 1 is found t o be dependent on t h e tacticity of PMMA. W e also examined t h e dependence of t h e fluorescence intensity of 1 i n solid PMMA films o n temperature. T h e transition a t -43 "C for i-PMMA was clearly observed and is consistent with unwinding of a helix.
Experimental Section
h Figure 1. Chemical structure of stereoregular poly(methy1 methacrylate). conformational structure of these macromolecules is still a m a t t e r of debate.4J*13 Liquori a n d co-workers4 proposed a fivefold helical conformation for isotactic PMMA, with a repeat distance of 10.4 A. However, Tadokoro a n d co-workers,12 using X-ray data, derived a double-helical structure, in which each s t r a n d consists of t e n r e p e a t units p e r t u r n , with repeat distance of 20.8 A. Recently, S ~ n d a r a r a j a n , using '~ virtual bond analysis, showed that t h e isolated 10-unit helix is, indeed, of lower energy t h a n t h e 5-unit helix by about 2.8 kcal/mol. Furthermore, t h e transition of 43 O C exhibited by isotactic PMMA was suggested t o be d u e to chain transformation from (5/1) to (5/2) helix by Liquoril0J1 and to transition between t h e (5/2) t o (10/2) helices by Sundararajan.13 Evidently, an alternative method for determining t h e conformational structure of stereoregular polymers is still needed. S u c h a technique should probe t h e microstructure of t h e polymer and account satisfactorily for t h e dynamic structural changes occurring over a wide t e m p e r a t u r e range. A t the same time, the measurement should not induce modification in t h e chemistry o r s t r u c t u r e of t h e polymer a n d i t should be simple. I n recent years t h e application of luminescence spectroscopy for t h e s t u d y of great diversity of p h e n o m e n a occurring in synthetic a n d n a t u r a l polymers has become w i d e ~ p r e a d . ' ~ - ' ~T h e versatility a n d sensitivity of luminescence as a technique in polymer chemistry stem from t h e multiple aspects of t h e interaction of electronically excited states with their immediate environment. We have recently described a novel p h e n o m e n o n associated with t h e effect of media rigidity on t h e fluorescence intensities of a series of donor-acceptor dyes, [p-(dialky1amino)benzylidene]mal~nonitriles.~~ T h e singlet-excited-state lifetime of these dyes is estimated to be 3-10 ps in solution, which corresponds to a nonradiative decay rate, k,, of t h e
Materials. Julolidinemalononitrile (1) was purified as described previously.20 Atactic poly(methy1methacrylate) samples were obtained from Polysciences Inc. as standards with narrow molecular weight distribution. Isotactic poly(methy1 methacrylates) were obtained by polymerization of methyl methacrylate using phenylmagnesium bromide or lithium aluminum hydride initiator^.^^-^^ Syndiotactic poly(methy1 methacrylate) was prepared as described elsewhere2* using ethyl(pentamethy1eneimin0)magnesiw-n initiator. All polymerizations were carried out in an inert atmosphere with syringe technique. The reactions were quenched by precipitation in a large excess of methanol containing a small amount of HCl and the solids filtered, washed, and dried. The crude products were then stirred in 10% aqueous HC1 solution, washed thoroughly with water, dried, dissolved in benzene, and freeze-dried. Molecular Weight Determination. The intrinsic viscosity, [ 71, of all polymers studied was determined in chloroform at 30 "C with a dilution viscometer. Molecular weight distributions and Mw's were determined by gel permeation chromatography, the latter being calculated as a Q factor. Tacticity Determination. Tacticities are expressed as triads on the basis of proton NMR spectra obtained on a Bruker WP-80 Fourier transform spectrometer. Spectra were obtained in nitrobenzene-d5 solution at 100-110 "C with Me4Si as internal standard. These analyses, along with the molecular weight data, are summarized in Table I, where i, h, and s are the fractional isotactic, heterotactic, and syndiotactic triad contents,respactively. Determination of the Glass Transition Temperature. The glass transition temperature Tgof each polymer studied was determined by differential scanning calorimetry using a Du Pont DSC apparatus. A typical DSC thermogram is shown in Figure 2. The thermal history of the sample greatly influenced the appearance of the first DSC curve. In general, several DSC runs were made with each polymer and the average of all runs was used to determine Tg.T,was obtained from the intersection of the initial base line and the sloping portion of the curve and is accurate to about *2 "C. The results are given in Table 11. The glass transition temperature of PMMA is strongly tacticity dependent. Our result is in fairly good agreement with literature data.25 Dye-in-Polymer Film Preparation. Films of the dye 1 (0.05 wt YO)in poly(methy1 methacrylate) were prepared by solvent casting from a 10% solution of solid polymer dissolved in methylene chloride. Typically 100 mg of PMMA was dissolved in 1 mL of 2 X M 1 in methylene chloride. Films were cast
454 Loutfy a n d Teegarden
Macromolecules, Vol. 16, No. 3, 1983 Table I Preparation of Stereoregular Poly(methy1 methacrylate) MMA initiator PMMA tacticity, triads %
stereoregularity isotactic
initiator PhMgBr LiAlH, PhMgBr free radical
atactic syndiotactic
M , x 10-3
MWD
1
61 80 82 75 81.8 250 90 180
3.2 1.8 3.2 1.04 1.75 1.04 2.3 1.3
>98 96 >98 6
EtMgN(CH,), EtMgN( CH,),
h
S
3
1
36
58
(approx the same) 23 23
~' The data in Table I1 show that dye 1 fluorescence is also sensitive to the tacticity of the polymer matrix. The quantum yield for fluorescence of 1 is markedly enhanced in isotactic poly(methy1 methacrylate) as compared to the syndiotactio or atactic polymers. The enhancement of fluorescence of 1 is caused by inhibition of the internal molecular rotation via rigidization of the probe by local environment. These results indicate that the flexibility of isotactic chains is lower than that of syndiotactic or atactic chains. Vitagliano and co-workersZ8have recently found that the probability of cationic dye (Acridine orange) intercalation in isotactic polyacids is much higher than that in syndiotactic ones. It is, therefore, tempting to speculate that the relatively high fluorescence yield of 1 in isotactic PMMA is due to rigidization of the probe by a helical conformation of the polymer chains. The motion of the intercalated dye molecules would be considerably impeded by the polymer, resulting in the enhancement of fluorescence. We have also examined the effect of temperature on the fluorescence of julolidinemalononitrile (1) in poly(methy1 methacrylate) films to probe the torsional relaxation processes of the various polymers over a wide temperature range. Figure 4 shows the temperature dependence of the fluorescence intensity, I F , of 1 in isotactic PMMA. A remarkable resemblance of the I F vs. T plot to the DSC thermogram of isotactic PMMA is observed; that is, a well-defined transition occurs at 43 "C.The temperature dependence of the fluorescence of 1 in syndiotactic or atactic PMMAlg is somewhat different from that in isotactic PMMA. The fluorescence intensity of 1 in syndiotactic (or atactic)Ig PMMA decreases gradually with increasing temperature, as shown in Figure 5. A break in the IF vs. T plot occurs at the glass transition temperature
D
Figure 5. Effect of temperature on the fluorescence of 1 in syndiotactic and isotactic PMMA.
of the polymer, 125 "C for syndiotactic and 106 "C for atactic PMMA. The decrease in fluorescence of 1 in syndiotactic and atactic PMMA with increased temperature is due to increase in polymer chain motion creating sufficient free volume for the probe to rotate. Above the glass transition temperature significant segmental motion of the polymer chains occurs, permitting the probe to rotate freely. At such a point the fluorescence intensity levels off and approaches that in fluid media. The fluorescence-temperature behavior of 1 in isotactic PMMA is radically different. A sharp drop in the fluorescence occurs at -43 "C, followed by the normal decrease in IF with increased temperature. This transition cannot be a glass transition but is rather consistent with a change in the conformation of the polymer chains from a tight, less flexible, to an open, more flexible, conformation. The types of relaxation that take place in amorphous polymers in the temperature range of interest here are (1) localized main-chain motions involving the cooperative but restricted motion of segments of few contiguous monomer units (processes usually have activation energies in the neighborhood of 10 kcal/molB) and (2) side-group motions such as methyl or ester groups, which tend to have smaller activation energies in the region of 2-4 kcal/mol. The activation energy for the relaxation process of isotactic PMMA at temperatures below 43 "C is 4.2 kcal/mol, consistent with side-group motion. Above 43 "C, the activation energy is 8.5 kcal/mol, which corresponds to localized main-chain motions. On the basis of the above information, one must conclude that the conformational transition at 43 "C for isotactic PMMA is triggered by rotations of the side groups, which change the choice of the preferred conformation. S ~ n d a r a r a j a n , 'on ~ the basis of virtual bond analysis, suggested that the conformational transition at 43 "C corresponds to transition between 5(2) and lO(2) helices. The fluorescence results presented here are in full agreement with this model. One final note on the apparent frequency independence of polymer transitions measured by the fluorescence technique is in order. For instance, the glass transition
Macromolecules 1983, 16, 456-462
456
temperature determined by our probe (relaxation frequency 10” Hz) agrees well with those determined by slow thermal relaxation techniques. The answer to this question lies in the fact that molecular and submolecular motions to which the probe is sensitive contribute to the macroscopic behavior of the polymer. In addition, the steadystate fluorescence measurements average out the macrodynamic behavior of the polymer chains. Basically, two principal findings have emerged. One is the dependence of the fluorescence yield of molecular rotors on the tacticity of the polymer matrix. The other is the sensitivity of the fluorescence of molecular rotors to dynamic changes in the conformation of polymers over wide temperature ranges. One must remember that different relaxation techniques applied to polymeric materials respond with different sensitivity to the various types of molecular motion. The fluorescence probe method complements many of the well-established methods of polymer material research.
(8) Gall, W. A.; McCrum, N. G. J . Polym. Sci. 1961, 50, 489. Plazek, D. J.; Rahgupath, N. Polym. Prepr., Am. Chem. Soc., Diu. Polym. Chem. 1974, 15, 53. (9) Bovey, F. A.; Tiers, G. V. D. J . Polym. Sci. 1960, 44, 173. Hatada, K.; Kitayama, T.; Okamoto, Y.; Ohta, K.; Umemura, Y.; Yuki, H. Makromol. Chem. 1978, 179, 485. (10) D’Alagni, M.; DeSantis, P.; Liquori, A. M.; Savino, M. J . Polym. Sci., Part B 1964, 2, 925. (11) Anzuno, 4.; Coiro, V. M.; D’Alagni, M.; DeSantis, P.; Liquori, A. M.; Savino, M. Nature (London) 1965,206, 358. (12) Kusanagi, H.; Tadokoro, H.; Chatani, Y. Macromolecules 1976, 9, 531. (13) Sundararajan, P. R. Macromolecules 1979, 12, 575; =nmrepresents the helix with n units in m turns”. (14) Beavan, S. S.; Hargreave, J. S.; Phillips, D. Adu. Photochem. 1979, 11, 207. (15) Morawetz, H. Science (Washington,D.C.) 1979, 203, 405. (16) Winnik, M. A.; Redpath, T.; Richard, D. H. Macromolecules 1980, 13, 328. (17) Semerak, S. N.; Frank, C. W. Macromolecules 1981,14, 443. (18) Johnson, G. E.; Good, T. A. Macromolecules, submitted for
publication.
(19) Loutfy, R. 0.; Law, K. Y. J . Phys. Chem. 1980, 84, 2804; Macromolecules 1981, 14, 587. Loutfy, R. 0. Zbid. 1981, 14, 270; J . Polym. Sci., in press. (20) Kuder, J. E.; Limburg, W. W.; Pochan, J. M.; Wychick, D. J . Chem. Soc., Perkin Trans. 1977,2, 1643. (21) Crescenzi, V.; D’Alagni, M.; Liquori, A. M.; Picozzi, L.; Savino, M. Ric. Sci. 1963, 33 (ZZ-A),123. (221 W. H.: . , Goode. W. E.: Owens. F. H.: Fellmann. R. P.:. Svnder, Moore; J. E. 2. Polyh. Sci.’1960, 46, 317. (23) Gocde. W. E.: Fellmann, R. P.: Owens, F. H. “Macromolecular Synthesis”; Wiley: New York, 1963; Vol. 1, p 25. (24) Joh, Y.; Kotake, Y. Macromolecules 1970,3, 337. (25) Thompson, E. V. J. Polym. Sci., Polym. Phys. Ed. 1966,4,199. (26) Melhuis, W. H. J . Opt. SOC.Am. 1964, 54, 183. (27) Nishijima, Y. J . Polym. Sci., Part C 1971,31, 353. Tredwell, C. J.; Osborne, A. D. J. Chem. Soc., Faraday Trans. 2 1980,12, 1622. Taylor, J. R.; Adams, M. C.; Sibbett, W. Appl. Phys. 1980, 102, 847. Jarandias, J. J . Photochem. 1980, 13, 35. Karstens, T.; Koh, K. J. Phys. Chem. 1980,84,1871. Jones, G.; Jackson, W. R.; Halpern, A. M. Chem. Phys. Lett. 1980, 72, 391. (28) Vitagliano, V.; Costantino, L.; Sartorio, R. J . Phys. Chem. 1976, 80, 959. (29) Allan, S. In “Molecular Basis of Transitions and Relaxations”; Meier, D. J., Ed.; Gordon and Breach Science: London, 1978; p 20.
Acknowledgment. We are in debt to Drs. S. Sundararajan and T. Smith for many useful discussions. Registry No. 1,58293-56-4; atactic PMMA, 9011-14-7; isotactic PMMA, 25188-98-1.
References and Notes (1) “Macromolecular Synthesis”; Overberger, C. G., Ed.; Wiley: New York, 1963; Vol. 1, p 29. Abe, H.; Imai, K.; Matsumoto, M. J. Polvm. Sci., Part C 1968, 23, 469. (2) Kawasaki-, A.; Furukawa, J.; Tsuruta, T.; Inoue, S.; Ita, K. Makromol. Chem. 1960,36, 260. (3) W. E.: Owens. F. H.: Fellmann. R. P.: Svnder. W. H.; . ~ Goode. . Moore; J. E. 2. Polym. Sci. 1960,56, 317. Iwamko, R.; Ohta; K.; Mimo, S. J . Polym. Sci., Polym. Lett. Ed. 1979, 17, 441. (4) D’Alagni, M.; DeSantis, P.; Liquori, A. H.; Savino, M. J. Polym. Sci., Part B 1964, 2, 925. (5) Fox, T. G.; Garrett, B. S.; Goode, W. E.; Gratch, S.; Kincaid, J. F.; Spell, A.; Stroupte, J. D. J. Am. Chem. SOC.1958, 80, 1768. (6) Shetter, J. A. J . Polym. Sci., Part B 1963, 209. (7) Steck, N. S. SPE Trans. 1964, 4, 1.
Effect of Different Shielding Groups on the Polyelectrolyte Behavior of Polyamines R. Barbucci,* M. Casolaro, and N. Danzo Istituto di Chimica Generale, 53100 Siena, Italy
V. Barone Zstituto Chimico, 80134 Napoli, Italy
P. Ferruti and A. Angeloni Zstituto di Chimica degli Zntermedi, 40136 Bologna, Italy. Received June 8, 1982
ABSTRACT: T h e stepwise protonation of three polymeric amines, containing a different shielding group between the amine moieties of the repeating units, has been studied from a thermodynamic standpoint. This was done for comparison purposes with structurally related poly(amido amines) whose monomeric units had been previously found to behave independently toward protonation. This study was performed by potentiometric and calorimetric techniques, and specific methods for the treatment of either “sharp” or “apparent” thermodynamic functions in polyelectrolyte having more than one basic group in the repeating unit have been developed.
Introduction The thermodynamic functions for the protonation of polymeric bases usually depend on the degree of protonation of the macromolecule (Le., on its total charge).’ Up to now, in only two classes of polymers, poly(amido amines)2and poly(ma~rocycles),~ have the monomeric units behaved independently toward protonation, thus giving 0024-9297/83/2216-0456$01.50/0
rise to “sharp” thermodynamic function^.^ (”Sharp”means that the thermodynamic functions do not depend on the degree of protonation (a)of the whole macromolecule, and “apparent” means that they do.) In order to gain further insight into the structural reasons of this unusual trend, we have modified the monomeric units of poly(amido amines) in several respects2Yb8 0 1 9 8 3 American Chemical Society
